1. Field of the Invention
The present invention relates to a laser beam generation apparatus to be used, for example, for a laser processing apparatus, semiconductor device inspection apparatus, interference meter, particle counter and laser display unit or the like.
2. Description of the Related Art
Research and development have been conducted widely for a laser light source to be used for a laser processing apparatus, semiconductor device inspection apparatus and others. A laser beam generation apparatus to be used for the above apparatuses can be classified into a side pumping system and end pumping system. The former is mainly used for a high output laser providing an average output of 10 W or more, while the latter for a laser providing an average output of 1 W or less. These systems respectively have the characteristics of the possibility for improvement in scale for higher output and good efficiency.
However these systems respectively have the advantages not competing with each other from the technical viewpoint but on the other hand have respective disadvantages.
For example, in the case of the side pumping system, draining of heat is difficult due to its lower efficiency and moreover an AR (No-reflection) coating is required for the plane of incidence for the laser medium pumping light beam.
In addition, the end pumping system has a problem that the surface of the laser medium requires a complicated coating and a structure of resonator is also restricted for the focusing of pumping light beam in order to satisfy a couple of performances that the pumping light beam is transmitted while the laser beam is reflected.
Problems of the related systems explained above will then be explained in detail. A single stripe semiconductor laser (manufactured by Polaroid Inc., USA) which is currently available provides the maximum output of 4 W and light emission width of 200 xcexcm (a Sony product assures light emission width of 300 xcexcm or 2 to 4 W/200 xcexcm and higher output will be expected in the future from narrower light emission width).
However, when a semiconductor laser oscillating near 809 nm and providing an output of 3 W is used for the end pumping system of Nd:YAG laser, an output of 1 W or more and 1064 nm can be obtained. In an experiment, an output of 1.3 W and 1064 nm can be obtained from the incident pumping beam power of 2.5 W. Namely, this output has been obtained through the process that an output beam of the semiconductor laser is collimated by a lens, the beam is then shaped with anamorphic prisms, the beam is then focused to generate a spot of 200 xcexcm in diameter within a laser medium and thereby good overlapping is realized with the resonator TEM00 mode in diameter of about 300 xcexcm. However, since the pumping light beam is incident via one end mirror forming a resonator in the end pumping system, there are problems that the laser medium must be provided near the end mirror and the end mirror itself must have higher transmissivity for the pumping light beam and requires at its rear surface the non-reflection coating for the pumping light beam.
Meanwhile, various examples have been proposed for the side pumping system and each example respectively introduces a structure that a semiconductor laser called a bar type or a semiconductor laser joined to a fiber are used and the pumping laser beam is incident in a vertical direction to the laser medium.
However, in the case of the Nd:YAG laser, if the no-reflection coating is not utilized, the Fresnel reflection loss becomes about 10% and the pumping light beam is not incident to the laser medium effectively. Moreover, the semiconductor laser explained above is often used when it has an output of several watts or more.
For realization of a laser actually providing an output of 1 to 2 W, the semiconductor laser of the bar type as explained above is not preferable from the viewpoint of the draining of heat. A bar type semiconductor laser has an output as high as 20 W but its power consumption is also as high as 40 to 60 W. When the laser is operated at a low output condition by reducing a current value, heat generated by the threshold value current reaching about 20 W must be eliminated, and therefore a cooling means such as a water cooling device is essential.
In more practical applications, for realization of output up to 1 to 2 W, it is more practical to use a semiconductor laser having an output of 3 to 4 W and it is advantageous from the viewpoint of draining of heat. These semiconductor lasers typically generate light beams assuring the light emission width of 200 to 300 xcexcm and low condensation property in the multiple mode in a width direction.
On the other hand, the light emitting area in the direction vertical to such a width direction is about 1 xcexcm and output light beam is the beam at the diffraction limitation having good condensation property. Therefore, when the output beam of these are collimated and condensed with an ordinary lens, such a flat beam as focusing the light emitting area in the light emission width direction and condensing in the vertical direction to such width direction can be obtained. Polarization of the output beam of the broad area semiconductor laser is parallel to the light emission width direction.
The present invention has been proposed considering the background explained above and it is therefore an object of the present invention to provide a laser beam generation apparatus including a solid state laser medium having a set of optically polished planes provided opposed with each other for allowing the laser beam to be pumped to pass and at least one optically polished plane different from above planes and a pumping beam source for emitting a pumping light beam for pumping the laser medium, whereby the pumping light beam to be incident from at least one optically polished plane different from a set of optically polished planes allowing the laser beam to be pumped to pass is incident to the laser medium in the incident angle equal to or similar to the Brewster angle.
According to one aspect of the present invention, the pumping light is an output light beam of a broad area semiconductor laser and the output light beam of broad area semiconductor laser is focused, using a focusing means of a lens and/or reflecting mirror, to the area near at least one optically polished plane which is different from an optically polished plane provided opposed with each other allowing the laser beam to be pumped to pass in the longitudinal direction of the light emitting aperture of the broad area semiconductor laser and is also condensed within the laser medium in the direction almost vertical to the longitudinal direction.
Moreover a first reflecting means reflects at least a part of the laser beam to be pumped which is incident to the laser medium to the laser medium in the reflection angle equal to or similar to the Brewster angle from the opposing plane which is almost parallel to the plane where the pumping light beam is incident and is optically polished and a second reflecting means for inputting again, in the reflection angle equal to or similar to the Brewster angle, at least a part of the pumping light beam reflected by the first reflecting means from the plane where the pumping light beam of the laser medium is incident are also comprised.